The proposed exploratory experiments will assess schedule-induced aggression in a simulated natural feeding situation (open food economy) in which pigeons work to procure their daily meals in anticipation of a significant biological deficit with attack that occurs in a traditional operant paradigm (closed economy) in which chronically deprived birds work to obtain only a portion of a meal during a daily feeding period. In both situations, birds will live in individual test chambers with aggressive behavior toward a conspecific image, operant responding, and meal patterns (when appropriate) continuously recorded as a function of the cost (effort and time) of procuring meals or a portion of one. We expect that schedule-induced attack will occur in the open food economy and that its relation to food availability will be similar to that which occurs in the closed economy and to aggression under natural feeding conditions. Such results would suggest that schedule-induced aggression in pigeons is a general effect of restricted availability of a reinforcer and that is a part of the bird's normal feeding strategy.